Floor covering

ABSTRACT

The present invention relates to sheet materials suitable for use in or as a floor covering. The sheet materials comprise a polyalkene resin in intimate admixture with at least one additive comprising a filler, wherein the polyalkene resin has a relatively narrow molecular weight distribution (MWD) and, a small amount of long chain branching and produced by a single site catalysed polymerisation of at least one, linear, branched or cyclic, alkene having from 2 to 20 carbon atoms. The present invention also extends to processes for the production of such sheet materials and floor coverings.

[0001] The present invention relates to floor coverings and moreparticularly to durable tile or sheet form floor coverings made of oneor more layers of polymers suitable for e.g. pedestrian traffic indomestic and/or other situations over an extended period of time.

[0002] Most floor coverings of this type are based on polyvinylchloride(PVC) polymer. In more detail, PVC polymer resin is generally mixed witha plasticiser (solid or liquid) (usually with various other additivessuch as fillers, polymer stabilisers, and processing aids) to form aspreadable paste which can be formed into sheets by spread coating usingknife or roller coater equipment and then thermally cured e.g. by ovenheating.

[0003] The use of PVC does however raise significant environmentalproblems due to the use of chlorine and there is accordingly a need forfloor coverings based on alternative polymers. Polyalkene polymers aregenerally preferred from an environmental point of view but the use ofconventional polyalkenes presents significant processing problems andthey are not suitable for use in floor covering manufacturing facilitiesbased on spread coating and calendering technology. In addition aparticular problem in employing conventional polyalkene polymers infloor coverings, is that they do not provide the necessary physicalcharacteristics required in the final product. In more detail floorcoverings produced using conventional polyalkenes have been known togive insufficient tensile and tear strength, abrasion and stainresistance, and elastic recovery.

[0004] It is an object of the present invention to avoid or minimize oneor more of the above disadvantages.

[0005] It has now been found that a particular class of polyalkenes,which are produced by single site catalysed polymerisation, can besuccessfully used in floor covering manufacture based on more or lessconventional spread coating or calendering technology. Moreparticularly, suitable polyalkenes in accordance with the presentinvention are those having a relatively narrow molecular weightdistribution (MWD) and, a small amount of long chain branching andproduced by single site catalysed polymerisation, and having thefollowing characteristics:

[0006] a) Melt Index (MI) of from 0.1 to 100

[0007] b) Density of from 0.86 to 0.97; and

[0008] c) a DRI of from 0.1 to 6.0, preferably from 0.4 to 5.5.

[0009] As used herein the following terms have the meanings indicated:

[0010] Melt Index (MI) or I₂ is the amount (in grams) of polymer resinwhich is extruded in a predetermined period of time (10 minutes) asmeasured in accordance with ASTM (American Standard Testing Method)D-1238 (190/2.16).

[0011] Molecular Weight Distribution (MWD) is the ratio of weightaverage molecular weight (Mw) to number average molecular weight (Mn)(i.e. Mw/Mn).

[0012] Density is the mass (in grams) of 1 cubic centimetre of resin asmeasured in accordance with ASTM D-792 standard.

[0013] Dow Rheology Index (DRI) is an index of long chain branchingmeasured by comparing the shift to the right (due to a longer relaxationtime), relative to a polymer resin with zero long-chain branching (LCB),in a plot of zero shear viscosity against relaxation time (both from across viscosity equation).

[0014] Other abbreviations used herein which are common in the artinclude:

[0015] PHR—parts per hundred parts by weight of polymer resin (orprincipal polymer resin component).

[0016] Suitable polyalkenes in accordance with the present invention mayalso comprise a polyalkene having a relatively narrow molecular weightdistribution (MWD) and, a small amount of long chain branching andproduced by a single site catalysed polymerisation of at least one,linear, branched or cyclic, alkene having from 2 to 20 carbon atoms.Conveniently the polyalkene comprises a copolymer produced bycopolymerisation of two or more alkenes comprising a first linear orbranched, alkene having from 2 to 8 carbon atoms and, a second, linear,branched or cyclic, alkene having from 2 to 20 carbon atoms. This allowsfor greater design flexibility in relation to obtaining sheet materialswith particular desired combinations of physical characteristics. Ingeneral there may be used up to 15 mole percent of said second monomer.It will of course be understood that where cyclic alkenes are used thesemay nave more than one carbon ring and thus include bicyclic andtetra-cyclic alkenes such as norbornene and tetracyclododecene.

[0017] In another aspect the present invention provides a sheer materialsuitable for use in or as a floor covering and comprising a polyalkeneresin in intimate admixture with one or more additives selected from afiller and a spread coating processing aid, wherein said polyalkeneresin has a relatively narrow molecular weight distribution (MWD),preferably less than 3.0, and, a small amount of long chain branchingand produced by single site catalysed polymerisation, and having thefollowing characteristics:

[0018] a) Melt Index (MI) of from 0.1 to 100

[0019] b) Density of from 0.86 to 0.97; and

[0020] c) a DPI of from 0.1 to 6, preferably 0.4 to 5.5.

[0021] One of the very versatile features of metallocene catalysts isthe range of comonomer which may be incorporated into polymeric chainsby using such catalysts in the single site polymerisation of alkenes.Metallocene catalysts are, or example, capable of incorporating intopolymer chains cyclic monomers, advantageously polycyclic monomers,including cyclic monomers such as norbornene (C₇H₁₀). Thus, for exampleit is possible to incorporate materials such as norbornene intocopolymers with ethylene, which has the benefit of raising the toughnessand melting point over conventional PE resins.

[0022] The new sheet materials provided by the present invention havethe further advantage of suitability for incorporating various designfeatures. It may be possible to incorporate graphic images into theflooring in a manner which will give an image with depth perception.Systems using ion projection technology are well known in the art. Thesesystems use an electrostatic charge corresponding to the desired image.This image is deposited on the material with a drum or belt. Thematerial bearing the electrostatic image is moved through a developerstation where a toning material opposite charge adheres to the chargedareas of the dielectric surface to form a visible image. Another layerof polymer may be deposited on top of this, and another image producedin this layer. By adding successive layers, each with its own image, itis possible to built a structure with an image depth perception. Thisart, using conventional resins, is explained in U.S. Pat. No. 5,347,296.

[0023] One advantage of using polymer prepared usingmetallocence-derived catalysts comes about during the image process.More particularly the use of metallocene catalysts permits theincorporation of boron containing end groups and/or very high levels ofunsaturation. These end groups may be functionalized to provideadditional means for facilitating imaging. Images may be created eithervia electrostatic projection systems or by functionalizing these endgroups so the polymer chains will better combine with toner or pigments.

[0024] In another aspect the present invention provides a sheet materialsuitable for use in or as a floor covering and comprising a polyalkeneresin in intimate admixture with at least one additive comprising afiller, wherein said polyalkene resin has a relatively narrow molecularweight distribution (MTD) and, a small amount of long chain branchingand produced by single site catalysed polymerisation of a first, linearor branched alkene having from 2 to 8 carbon atoms and, preferably asecond, linear, branched or cyclic, alkene having from 2 to 20 carbonatoms.

[0025] Whilst processing aids may be used in the new materials of thepresent invention, to adjust or accentuate particular processingcharacteristics such as reduced energy requirements and/or increasedprocessing speed, it is a feature of the polyalkene resins used in thepresent invention that they do not require the use of a plasticiserthereby significantly reducing environmental problems caused by themigration of liquid plasticizers out of the material and/or loss ofperformance associated with the use of plasticisers.

[0026] Nevertheless, in those cases where it is desired to increaseprocessability, then there may be used a processing aid or plasticiser,and it is an advantage of the present invention that a significantlysmaller amount of plasticiser can be used as compared with polymerresins conveniently used in floor coverings. In a particularly preferredform of the invention there is, moreover, used a plasticiser orprocessing aid comprising a selectively polymerisable liquid monomersystem which is substantially non-polymerisable under the sheet forming,e.g. extrusion, spread-coating or calendering, conditions used in thefloor covering sheet material manufacturing process whilst beingsubstantially polymerisable subsequently so as to produce a materialsubstantially free of liquid plasticiser. In general the polymerisablemonomer may be used in an amount relative to the polyalkene resin offrom 20 to 80:80 to 20. Further details of suitable plasticisers arediscussed hereinbelow.

[0027] In this connection it will be understood that there is normallyused an initiator substance in order to induce polymerisation of themonomer and which is included together with the monomer in the monomersystem. Accordingly in such cases it is important that the initiator isone that is selectively activatable i.e. is substantially inactive underthe polyolefin product forming conditions but may subsequently beactivated under suitable plasticiser monomer polymerisation or curingconditions.

[0028] Various polyalkene resins suitable for use in the materials ofthe present invention are known in the art. In general they are producedby polymerisation of alkene monomers in the presence of particularcatalysts which restrict the progress of the polymerisation and areknown as metallocenes (the resulting polymers being commonly referred toas metallocene polyolefines conveniently abbreviated as MPOs). Suchpolyolefines and processes for their production are described in, interalia, U.S. Pat. No. 5,272,236.

[0029] Preferred polyalkenes that may be mentioned comprise copolymersof ethylene and an alpha-alkene having from 4 to 20 carbon atoms,advantageously from 4 to 10 carbon atoms, for example propylenebutene-1, or hexene-1, or a cyclic olefine such as norbornene;copolymers of propylene and an alpha-alkene having from 2 to 10 carbonatoms, for example butene-1, hexene-1, of a cyclic olefine such asnorbornene; and copolynmers of 4-methyl-1-pentene and an alpha-alkenehaving from 2 to 10 carbon atoms, for example, butene-1, hexene-1, or acyclic olefine such as norbornene. Preferably there is used a copolymercontaining up to 15 mole percent of comonomer. It will moreover beappreciated that there may be used more than one comonomer, that is,there may for example be used a terpolymer wherein are employed twodifferent alpha-alkenes each having from 2 to 20 carbon atoms.

[0030] Suitable polyalkene resins that are commercially available fromthe Exxon Chemical company of USA and the Dow Chemical company ofMidland, Mich., USA, are listed in Tables 1 and 2 below. TABLE 1 Exxon'sEXACT (TM) Resins Product Key Properties EXACT 3017 Density 0.901 MI 27EXACT 3025 Density 0.910 MI 1.2 EXACT 4038 Density 0.885 MI 125 EXACT4041 Density 0.878 MI 3.0 EXACT 5008 Density 0.865 MI 10 EXACT 4006Density 0.880 MI 10.0 EXACT 4003 Density 0.895 MI 9.0 EXACT 4023 Density0.882 MI 35.0 EXACT 4033 Density 0.880 MI 0.80

[0031] TABLE 2 Dow's INSITE (TM) TECHNOLOGY POLYMER (ITP) Product KeyProperties Engage CL8200 Density 0.870 MI 5.0 DRI 0.5 Engage CL8150Density 0.868 MI 0.5 DRI 2.0 Affinity SM1300 Density 0.902 MI 30.0 DRI0.4 Affinity SM1250 Density 0.885 MI 30.0 DRI — Engage LG 8005 Density0.870 MI 1.0 DRI 2.0

[0032] In a further aspect the present invention provides a polymerresin-based floor covering comprising at least one layer of a sheetmaterial of the invention. It will be appreciated that in general suchfloor coverings comprise two or more different layers having particularfunctions, bonded together. Typically there may be included layers suchas a foamed layer to provide cushioning; a structural layer comprising areinforcing carrier or substrate impregnated and/or coated with asaturant formula; a solid backcoat layer; and a clear protective ortopcoat layer.

[0033] For some types of applications little or no expansion in some orall layers of the floor covering structure will be required. The currentinvention includes a range of floor covering systems from those whereinall layers, except the topcoat, are foamed to those where none of theconstituent layers are foamed.

[0034] The sheet materials of the invention may be produced by a processcomprising the steps of:

[0035] providing a suitable polyalkene resin in accordance with thepresent invention and at least one additive comprising a filler andoptionally a sheet formation, typically a spread coating or calendering,processing aid;

[0036] bringing said polyalkene resin into intimate admixture with saidat least one additive in a high shear mixer for a period of at least 10minutes at an elevated temperature to at least 75°, preferably from 100to 250° C., most preferably from 130 to 200°, for melting thepolyalkenes and sufficient to bring the mixture into a substantiallyfluid state without substantial degradation of the mixture;

[0037] forming the fluid mixture into a sheet form; and

[0038] allowing said sheet to cool and solidify.

[0039] In one preferred aspect of the invention there is used a saidfluid mixture which is substantially free of any plasticiser.Nevertheless, as discussed elsewhere herein, there may be included inthe mixture one or more plasticisers or processing aids. Where there isused a polymerisable plasticiser, then the process includes furthertreatment of the solidified sheet in order also to solidify theplasticiser. Where a fugitive plasticiser is used the processadvantageously includes the step of volatilizing said plasticiser.

[0040] The sheet material production processes of the present inventionhave significant advantages over those made using conventionalpolyalkene or polyolefin resins. Apart from the superior processabilitywhich allows the use of conventional existing production plantpreviously utilized for PVC resin based sheet materials with minimalmodifications, they also have lower energy consumption costs due to thesubstantially reduced curing temperatures required as compared with PVCresin based production which involve increasing temperature to effect athermal curing as opposed to a cooling to effect “crystallisationcuring” by “solidification”. Further benefits that can be obtained inrelation to particular floor covering layers in products of theinvention include better toughness of the outer clear coat layer withbetter impact resistance resulting from the lower crystallinityassociated with lower density; better cell recovery in foamed cushioninglayers; and better filler acceptance due to more homogenous nature ofthe polymer (narrow MWD); and good flowability of the saturated layerresulting from high MI with little or no comonomer blocking.

[0041] In relation to the various aspects of the present invention itwill be appreciated that other polymer resins outside those specifiedmay be used in admixture with the specified ones e.g. in order to“extend” the specified polyalkene resin for reasons of economy by usinga cheaper polyalkene resin, or to modify finish or othercharacteristics. The amount of such other polymer resin that may be usedwill depend primarily on how they affect the fluidity and spread coatingcharacteristics of the materials of the invention. Thus for examplethere may be used up to around 50 to 60% w/w of said other polymer resin(relative to the total polymer resin) depending on the required use andproperties of the sheet layer. Thus, for example, in relation to theclear coat layer, the amount of such other polymer resin would normallybe restricted to a lesser amount of not more than around 15 to 20% w/w.

[0042] Additives that may be used in the materials of the presentinvention and the amounts thereof, will depend on the function anddesired properties of the sheet material and may also, to some extent,depend upon the particular polymer resins used. Principal additives andadditional processing steps generally well known in the art, that may bementioned include the following:

[0043] 1. Inorganic fillers and reinforcements can enhance the variouspolyolefin based layer or layers in the floor covering material, whichis the subject of this invention. This enhancement can be throughimprovements in appearance, physical properties, or chemicalcharacteristics. The particular inorganic filler/reinforcementattributes that are important are the nature of the inorganic material,the shape of the material, and any surface treatment or coating. Thereare many important aspects of the inorganic material. Density isimportant in the application and long term utility of a floor covering.Highly filled back coat layers (e.g. up to 85% by weignt of filler) canbe very useful in this regard. Another basic material attribute ishardness. Increased hardness is desirable in the final product, but toohard a filler (such as silica) can have negative effects on the wear ofprocessing equipment, such as melt mixers and extruders. Table A listssome common inorganic fillers/reinforcers. TABLE A DENSITY HARDNESSINORGANIC MATERIAL g/cc MOBE SCALE Calcium Carbonate 2.7 3 Talc 2.9 1.5Mica 2.8 3 Glass Fibres 2.9 — Silica 2.5 7.0 Wollastonite 2.9 4.7Aluminium Trihydrate 2.4 3.0 Magnesium Hydroxide 2.3 2.0 TitaniumDioxide 4.2 7.0

[0044] Whiting filler is used to increase opacity. Generally there isemployed less than 500 PHR, preferably from 20 to 120 PHR in saturantformula and foamable cushioning materials and up to 200 PHR in solidbacking layers.

[0045] The optical properties of titanium dioxide make it a particularlygood pigment in obtaining a white colour with good opacity. Such acolour is desirable in the layer upon which the printed design isplaced. This is located below the transparent wear layer. Lower levelsof titanium dioxide (2 to 6 PHR) can be employed if a white filler suchas Calcium carbonate is used at moderate levels in this layer.

[0046] Calcium carbonate is of particular utility in polyolefin basedcompositions. Hardness, stiffness, heat deflection temperature, slipresistance, stress crack resistance, weldability, printability, andantiblock characteristics are all improved. Thermal shrinkage andelongation, as well as water vapour and oxygen permeability aredecreased.

[0047] Talc is another filler well suited to enhance polyolefinformulations for floor covering. It has a lamellar structure in contrastto the low aspect particulate structure of calcium carbonate. Thislamellar form allows talc to be more effective than calcium carbonatewith regard to increasing stiffness, heat deflection temperature anddimensional stability. The disadvantage of talc relative to calciumcarbonate centre on reduced impact strength, matt surface, and lowerthermooxidative stability. Mica also has a lamellar structure and hassimilar advantages and disadvantages.

[0048] High aspect ratio fillers/reinforcements such as wollastonite andglass fibres, have an even stronger effect than talc and mica onincreasing the modulus of elasticity, tensile strength, andheat-distortion temperature of polyolefin based systems.

[0049] The improvements provided by high aspect ratio inorganicadditives would be of particular assistance in these floor coveringsystems made using a permanent plasticizer or processing aid, such asliquid paraffin. In these cases, the stiffening action of such additiveswould compensate for the loss of stiffness produced by the liquidparaffin.

[0050] Silica in its fumed or precipitated forms can be useful at lowlevels (0.1 to 1.5%) in the polyolefin formulations where antiblockingand printability is of importance. In the floor covering system thesewould be in the wear layer and in the layer upon which the printeddesign is applied.

[0051] Alumina trihydrate and magnesium hydroxide, in the correctparticle sizes which for most systems are less than 40 microns indiameter, can provide the same type of property enhancement provided bycalcium carbonate. In addition, they can provide useful fire resistanceand smoke control characteristics. This will be discussed in more detailin the fire resistance section.

[0052] 2. Polyolefin materials for floor covering systems are enhancedby the use of the thermal and light stabilizers. For thermal stabilizersthe amount and type that should be used will vary with the actualprocess used to fabricate the final structure. The melt spreaderapproach will provide a product having less heat history than either themelt calendering or extrusion routes. In all cases that involve foamedsystems, however, the polyolefin resins will be exposed to temperaturesover 180° C. for some time during the process.

[0053] Suitable stabilisers include hindered phenol at from 0.05 to 0.30PHR, optionally with co-stabilisers e.g. organosulphur compounds such asDSTDP at from 0.2 to 1.0 PHR. More particularly good thermal stabilitycan be obtained in these polyolefin systems using a high molecularweight hindered phenol, such as Irganox 1010 from Ciba-Geigy, with oneor more secondary antioxidants such as thioethers and phosphoruscompounds. Distearylthiodipropionate (DSTDP) and Ultranox 626 from GEare examples of these types of materials. An effective thermalstabilizer package from such systems is 0.1% Irganox 1010, 0.1% DSTDPand 0.05% Ultranox 626.

[0054] Hindered amine light stabilizers (HALS) are particularlyeffective in protecting polyolefins from photo-oxidation. A PolymericHALS, such as Luchem HA-B18 from Atochem, is particularly effective inits own right and has the added advantage of showing no antagonism forother additives such as DSTDP. The inclusion of 0.3% of Luchem HA-B18 inthe outer wear layer and 0.15% in the layer just below the transparentwear layer will greatly enhance the light resistance of the subjectpolyolefin floor covering system.

[0055] 3. Lubricants and processing aids may be of assistance in themanufacture of the polyolefin based flooring system. This will be verydependent on the specific process. For extrusion or melt calenderingoperations an external lubricant may be of assistance. Calcium and zincstearate are appropriate as external lubricants. They also can providesome additional stabilization support. They can be added in the 0.1 to1.0%, preferably 0.2 to 1.0% range is needed.

[0056] 4. Depending on the spread coating or calendering process andconditions, melt strength enhancement of the polyolefin system may beuseful. Grafts of polyolefins and acrylics are useful at the 0.1 to 1.0%range in proving a stronger more elastic melt.

[0057] 5. In the polyolefin based floor covering which is the subject ofthis invention, for most applications it is desirable to have one ormore of the layers in the structure (but not the wear layer) to beexpanded in the form of a close cell foam. One effective route to suchan expanded layer is through the use of a chemical blowing agent. Inpolyolefin systems azo compounds are especially effective. An example ofthis class of compounds is Azodicarbonamide (Celogen AZ from Uniroyal).A particularly useful feature of this compound is that its decompositionpoint can be reduced from 220° C. to less than 170° C. through the useof activators, such as zinc oxide. This activated system can bedeactivated through the use of inhibitors such as benzotriazole. If inkscontaining benzotriazole are used to print on the surface of apolyolefin containing Celogen AZ and Zinc Oxide and the resultingstructure, with a wear layer added over the foamable layer, is heated totemperature between the activated and inactivated decompositiontemperatures, then a raised pattern (chemical embossment) is created inthe sample.

[0058] A supplemental blowing agent such as aluminum trihydrate may beemployed in these structures. Although its primary role is that of aflame retarding additive and inorganic filler it has a useful auxiliaryrole as a blowing agent in that it gives off water vapour when heatedabove 200° C. A volatile fugitive processing aid or plasticizer can alsohave a useful role as a supplemental blowing agent.

[0059] In the case of azodicarbonamide this is generally used forfoamable cushioning layers at from 2.0 to 4.5 PHR, together with asuitable foaming activator such as zinc oxide.

[0060] Some or all chemical blowing agents can be replaced withmechanical foaming, given the correct conditions. Such conditionsinvolve the mixing into the polyolefin based mixture, that will becomeone of the layers in the floor covering material, air or another gas,under conditions that will produce the desired number and size of cellsin the resulting foam. In the spread coating system the mixture asapplied needs to have a foam structure near to that of desired product.In the extrusion or calendering process the gas needs to be in solutionin the polymer or as small micro bubbles at the melt pressure in theextruder system. Expansion takes place as the melt leaves the extruderand goes from high pressure (100 to 700 PSI) to atmospheric pressure. Inboth cases, it is important for the cell structure to be frozen at thedesired size by a rapid drop in the sheet temperature to below thatneeded for cell contraction or deformation.

[0061] 6. The properties of the polyolefin structures in the subjectfloor coverings can be enhanced through the use of crosslinking,conveniently by means of an organic peroxide e.g. at from 0.1 to 5.0 PHRfor increasing toughness and/or stiffness of the sheet layer. Dicumylperoxide is a reagent used extensively for such reactions. This materialbecomes an effective crosslinking agent at 190° C. In the case ofcrosslinked foamed polyolefin systems it is known that a better foamcell structure is developed if the crosslinking is done before the foamis formed. In systems involving Celogen AZ for foaming and dicumyylperoxide for crosslinking, both processes would take place at the sametime and temperature. If a peroxide with a lower activation temperature,such as 2,2-bis (tert. butylperoxy) butane were used then thecrosslinking could be carried out at about 170° C. followed by a foamingprocess at 190° C.

[0062] The development of strong crosslinked filled foam polyolefinsystems can be further enhanced by treating the inorganic filler to beused with vinyl silane. The vinyl groups that become attached to thefiller particles become active in forming the cross linked networkinitiated by the peroxide produced free radicals.

[0063] In non-expanded layers Dicumyl peroxide would be a goodcrosslinking agent. In layers to be expanded, using 2,2-bis (tert.butylperoxy) butane in conjunction with an activated Celogen AZ blowingsystem would be desirable. In all filled layers to be foamed, the fillershould be treated with agent such as vinyl silane that will providesites of unsacuration on the filler particles.

[0064] 7. The flammability and smoke generation of the polyolefin basedfloor covering system is of importance. Fire characteristics can beimproved through a wide range or additives. Various inorganic compounds,such as aluminum trihydrate and magnesium hydroxide, that give off waterat elevated temperatures are useful as dual fillers/flame retardants.Phosphorous compounds, borates, and zinc oxide all can play useful rolesin improving the fire characteristics of polyolefin bases systems.

[0065] 8. polymer resins other than the specified MPOs may be used asnoted above as extenders or modifiers in amounts of from 10 to 30 PHR.Examples that may be mentioned include LLDPE (Linear Low DensityPolyEthylene), EVA (Ethylene Vinyl Acetate), Ionomers e.g. SURLYN (TM)available from the DuPont Company, and VLDPE (Very Low DensityPolyEthylene).

[0066] In addition, blends of two or more metallocene preparedpolyolefins may be used to obtain particular combinations of desiredproperties.

[0067] To improve impact properties various types of elastomericcomponent additives can be used in generally known manner. Thesegenerally comprise small particles with a core of an elastomer e.g.butadiene or acrylic polymer coated with an outer shell that willprovide good adhesion to the MPO polymer resin matrix. An example ofsuch an elastomeric component core/shell modifier additive is ParaloidEXL-330 from the Rohm and Haas Company. This resin has an acrylaterubber core and a polymethyl methacrylate shell. Other types ofmodifiers that can be used to enhance impact properties include EPDMrubbers, such as Polysar manufactured by Bayer; A/B/A block copolymers,such as Kraton manufactured by Shell; and multiple domain elastomersystems, such as those described in European Patent No. 583,926.

[0068] 9. Other additives that may be mentioned include dyes, inks,antioxidants etc. which are generally used in relatively small amountsat less than 50 PHR. Antistatic characteristics can also be importantfor some applications.

[0069] In this case, the use of various internal antistatic agents inthe wear layer would be appropriate. Many antistatic additives arecompounds with hydrophilic and hydrophobic sections. A common materialof this type is a mono ester of a polyol, such as glycerol, with a longchain fatty acid, such as stearic acid. The polyol portion is very polarand would come to the surface of a polyolefin, while the fatty acid is“polyolefin-like” and would stay within the plastic.

[0070] 9. The hydrophilic part can be cationic, anionic, or non-ionic.Levels of 0.1 to 0.5 PHR in the outer layer of the structure areappropriate.

[0071] 10. Carriers or substrates used with saturant formulations mayhave various forms e.g. woven or non-woven mesh or fabric, or tissue, ofmore or less thermally stable materials such as glass fibre.

[0072] The polyalkene or polyolefin resins used in accordance with thepresent invention may be of various different types including randombipolymers and terpolymers, and block copolymers, based on a variety ofmonomer units including lower alkene, preferably 1-alkene, having from 2to 8 carbon atoms e.g. propylene but most preferably ethylene; dienes;cycloalkenes; and vinyl aromatic compounds.

[0073] Further preferred features of the invention will appear from thefollowing detailed Examples given by way of illustration and theaccompanying schematic drawings in which:

[0074]FIG. 1 is a schematic side view showing a first part of a floorcovering production line; and

[0075]FIG. 2 is a similar view of the second part of the production lineof FIG. 1.

[0076]FIG. 1 shows a first-stage production line 1 for producing afirst-stage three layer sheet material 2 by applying saturant, foam gel,and back-coat layer formulations 3, 4, 5 onto a glass fibre tissue web(approx. 0.45 mm thick) 6 supplied from a supply drum 7 via a firstaccumulator 8. The tissue web is passed via a first weight/unit areameasuring system 9 to a first spread coating unit 10 at which the hotmelt saturant formulation 3 (at approx. 90° C.) is applied onto one side11 of a first roller 12 to a predetermined thickness of about 0.55 mmcontrolled by a first knife 13, from a first continuous high shearbarrel-type mixer 14. At the other side 15 of the first roller 12, thesaturant formulation is transferred to the tissue web 6 at a nip 16between the first roller 12 and an opposed tissue web support roller 17.The impregnated tissue web 18 is then passed around a large diameterchilled drum 19 set for a surface temperature of around 25 to 40° C. andfurther smaller diameter cooling drums 20 for “crystallisation curing”or solidification.

[0077] The hot melt foam and back-coat layer formulations 4, 5 are thensuccessively applied to the coated tissue web 18 at approximatethickness of 0.2 and 0.6 mm, respectively, in generally similar mannerat second and third spread coating units 21, 22, except that a largediameter chilled drum 1 is omitted at the back-coat layer stage. Theresulting three layer sheet material 2 is then collected on a wind-updrum 23 down-stream of a second accumulator 24. If desired this sheetmaterial is then passed to a rotogravure or other printing station forapplication of graphic design material etc. in generally known manner,for example, using ink designed for chemical embossing.

[0078]FIG. 2 shows a second stage production line 101 in which likeparts corresponding to those in FIG. 1 are indicated by like referencenumerals to which have been added 100. The three layer sheet material 2produced in the first stage production line 1 is supplied from a supplydrum 107 via an accumulator 108 to a fourth spread coating unit 110 atwhich a clear coat formulation 125 is applied to said sheet material 2at a thickness of about 0.2 mm, and cured as before except that in thiscase a heat shield 126 is provided between the chilled drum 119 and thehot mixer 114 to help improve temperature control etc.

[0079] If desired a further foamed back-coat layer may be applied usingyet another spread-coat applicator (not shown). It will incidentally beappreciated that in accordance with common practice in the industry theorder of application of the various layers can be varied to a greater orlesser extent.

[0080] Finally where a polish or lacquer type finish is required thiscan be applied using a grooved roller applicator 127.

[0081] The resulting multi-layer sheet material 140 is then passedthrough a multi-stage hot air oven 141 on a belt support 142 set to amaximum temperature of around 200° C. with a dwell time of around 1½minutes to allow foaming expansion of the foam layer (from about 0.2 mmto about 0.5 mm) with selective control thereof by chemical embossingwhere this is used, whereupon final cooling of the finished sheetmaterial takes place at further cooling drums 120 prior to collection onthe take-up drum.

[0082] Melt calendering can also be used to produce the floor coveringswhich are the subject of this invention. Although both rolling sheet andviscous blank calendering can be employed, rolling sheet is preferredwith a glass fibre web, being the preferred substrate.

[0083] A multilayer laminate is prepared by applying a series of meltsbased on the polyalkene or polyolefin resins as described in thisinvention. These melt calendering operations can all be done in acontinuous way using a series of calendering rolls, or they may be donein a segmented fashion with a single layer being applied followed by awind up operation with additional layers being added in separateoperations. In addition, a combination of continuous and discontinuouscalendering operations can be employed. Thus for example, a saturantformulation can be applied to a glass fibre web followed by a foamablelayer on top and a base layer beneath. These three operations beingcarried out in a consecutive way as the material passed through threedifferent sets of calender rolls before wind up. Additional processingsteps can be placed between and among calendering operations. Forexample, the material produced by applying three polymer layers to aglass fibre web could be passed through a printing process, to provide adecorative image and to facilitate chemical embossing. This distinctprinting step could be followed by another melt calendering step toapply a wear layer to the floor covering. A heat treatment step couldfollow the application of the wear layer, either in a continuous ordiscontinuous fashion. The heat treatment could expand the variouslayers through the formulation of a chemical foam, in those layerscontaining a chemical blowing agent. In addition, the physical andchemical properties of the polyolefin resins could be enhanced throughcrosslink formation in these layers via the use of a crosslinkingsystem.

[0084] In the melt calendering process, a polymer melt is applied to aseries of two or more heated rolls in such a way to produce a layer ofpolymer of uniform thickness. The melt is prepared by mixing thepolymers and non-polymeric components of the material under conditionsof elevated temperatures and shear. Devices such as extruders or mixerscan be used for this process. More detailed descriptions of the meltcalendering process can be found in Chapter 83 of “Handbook of PlasticMaterials and Technology” by Irvin I. Rubin and published by John Wilyand Sons, Inc (ISBN 0-471-09634-2)

[0085] The floor covering structure, which is the subject of thisinvention, can also be prepared by melt extrusion. In such a process,one or more polymer layers can be applied to a continuous glass fibreweb in a single extrusion operation. When co-extrusion is used toprovide multiple layers in a single pass, a separate extruder is used tofeed each melt to the sheet die block. Extrusion operations can beintermixed with other processing steps in preparing the final structure.For example, a glass web can be saturated and encapsulated between abase layer and foamable layer in single co-extrusion pass involving athree melt feed sheet die. This structure then can be subjected to aprinting process followed by a single layer being added by extrusion. Athermal treatment can follow the application of the wear layer in eithera continuous or discontinuous fashion. This treatment could enhance thefinal product by expansion of layers containing chemical blowing agentsand/or crosslinking of layers containing crosslinking systems.

[0086] The initially described process for developing the desired floorcovering structure through the use of a melt spreading approach, asshown in FIGS. 1 and 2, can be extended in scope through the use offugitive and/or permanent processing aids or plasticizers. This involvesthe addition of a liquid or liquids to the various polyolefinformulations used to make the discrete layers of the final structure.Such an addition can be used to lower the temperature needed to obtainthe viscosity needed for good processing. For example, white spirit,petroleum ether, or mineral spirits can be blended with a polyolefinlayer system using heat and shear mixing to produce a homogenous lowviscosity material which can be processed at a lower temperature thanwould otherwise be possible. This is a fugitive system as the whitespirit or other plasticiser evaporates from the surface of the structureafter the system has been applied. Preferably, the vaporized whitespirit or other plasticiser is captured, condensed, and recycled.Alternatively, a non-volatile liquid plasticiser, such as liquidparaffin (mineral oil) can be used. In this case, the resulting floorcovering structure will retain this material as a permanent component.Mixed systems of fugitive and permanent liquids can also be used. Therange for such additives can extend from 200% to less than 5%, on aweight basis of polyolefin. Most desirably though there is used apolymerisable plasticiser.

[0087] The polymerisable plasticiser monomers that can be used inaccordance with the present invention are those that are solvents forthe main polymer component(s) of the polyolefin product. They need not,and would normally not, be solvents for the inorganic components nor forother components, which may themselves also be polymers, such as impactmodifiers, texturing aids, pigments, and some compatibilizers. Themonomers will, in general, have a long segment that is “polyolefin like”with an end group that is capable of free radical polymerization.Typical “polyolefin like” structures are hydrocarbons with ten or morecarbon atoms, and examples of such groups would be lauryl (C₁₂H₂₅) andstearyl (C₁₂H₃₇). Such structures can be linear, branched, or cyclic;depending in part upon the structure of the polyolefin. The terminalpolymerizable group can be a simple unsubstituted double bond, such asin 1-dodecene or a more complex unit such as a methacrylate, as instearyl methacrylate.

[0088] Along with the plasticiser monomer or monomers, compounds thatgenerate free radicals at elevated temperatures and optionallycrosslinking monomers may be used to cure the resulting products and toprovide enhanced properties. Many classes of free radical generators canbe used, but materials in the peroxide, ketone peroxide,peroxydicarbonate, peroxyester, hydroperoxide, and peroxyketal familiesare of particular use. Also of utility are several classes of azocompounds and a variety of photoinitiators. The characteristics neededin these compounds is that they are substantially non-polymerisable i.e.remain essentially dormant during the initial mixing, compounding, andproduct fabrication process but can be induced to produce free radicalsat a rate that will initiate a polymerization of the monomer e.g. whenthe temperature is increased, or when exposed to the appropriateradiation. For example a material such as t-butyl perbenzoate has a halflife of over 1000 hours at 100 C, while having a half life of less than2 minutes at 160 C. In a polymer/monomer system containing such aninitiator it would be possible to process the system into the finishedproduct form (i.e. shape or configuration) at 100 C and then cure thesystem by a brief exposure at 160 C.

[0089] When polyfunctional monomers are included in the system when acontinuous crosslinked polymer system can be formed from the monomer.Optionally additional radical generators can be included that willprovide cross linking of the pre existing polyolefin system. A Semi-IPN(inter-penetrating network) is obtained when one of the co-continuoussystems (i.e. the pre-existing polyolefin and the polymerisedplasticiser monomer) is crosslinked. When both systems are crosslinkedan IPN is formed.

[0090] To prevent premature polymerisation of the plasticiser monomer itmay be useful to add additional inhibitors to the system. Mostcommercial monomers are provided with inhibitors to preventpolymerization during handling and processing. The level of suchinhibitors should be increased to compensate for the time spent underthe polyolefin polymer product forming conditions, i.e. the conditionsused to form the base polyolefin polymer into a sheet or some othershape or configuration. In this connection the temperature is usuallythe most significant factor, but other conditions may also be relevant.Thus for example stearyl methacrylate is commercially provided with 275parts per million (ppm) of the monomethyl ether of hydroauinone (MEHQ).Depending on the times and temperature involved 1000 ppm MEHQ, or more,may be needed. Inhibitors from a wide range of chemical families made beused for this purpose.

[0091] The polymeric system and the monomeric system can be combined ina variety of ways to give a low viscosity plasticised material that canbe used to manufacture many types of products using several differentfabrication techniques. The combination of the solid and liquidcomponents can be done in any suitable manner e.g. by using a continuousor batch mixer, various types of continuous and batch blending devices,and various types of extruders. In all these types of equipment thesolid components are mixed together at sufficient temperature and withsufficient shear to achieve both distributive and dispersive mixing. Theliquid is introduced at the needed temperature and shear to dissolve theprincipal polymeric components and to obtain good distributive mixingand dispersive mixing of the insoluble components with the resultingfluid. The fluid system is then held at a temperature that retains therequired fluidity for the fabrication of the final product form. Ingeneral this will usually be in the from 80 to 120° C.

[0092] It will be appreciated that polymerisation of the polymerisableliquid plasticiser will result in the creation of polymer chains whichextend through and interpenetrate the previously formed network of MPOpolymer chains. Where both the MPO polymer chains and the polymerisedplasticiser are cross-linked then the two polymer materials captivelyinterengage each other forming a so-called interpenetrating polymernetwork (IPN), whilst if only one of these is cross-linked, then thenon-cross-linked polymer chains could in principle be pulled out. Thelatter type of material is conveniently referred to as a semi-IPN. SuchIPN and semi-IPN materials, whilst having generally similar physicalproperties to those of the other novel materials provided by the presentinvention, offer further advantages in terms of improved stainresistance and/or increased resistance to solvents both duringinstallation and in use of the floor coverings provided by the presentinvention.

EXAMPLE 1 Preparation of Multi-Layer Floor Covering Using Calendering

[0093] A floor covering structure is prepared by first developing threelayers in a continuous melt calendering operation in a first stageproduction line (see FIG. 1). In this operation, a continuous glassfibre mat is fed into a through station calendering line. Each stationis fed by a separate melt mixer. At the first station, the glass mat issaturated with composition A. In the next station, the backing layer,composition B, is applied. In the third station, the foamable layer,composition C, is applied. The system is then taken up on a take uproll. In a separate operation this system is fed through a printing linewhere a decorative design is applied to the foamable layer. In a thirdprocessing step, this printed material is fed into single meltcalendering station in a second stage production line and then into atwo zone oven system (see FIG. 2). At the calendering station a cleartop coat, composition D, is applied. In the first zone of the oven,which is at 160° C. the crosslinking of each layer occurs; in the secondzone at 190° C. the expandable layer foams. The final product is thencollected on a take up roll.

[0094] The compositions of the various layers are as follows:- PHR A.(Saturant Layer) Exact 4038 MPO Resin 100 Magnesium Hydroxide Fireretardant 60 inorganic filler Dicumyl Peroxide free radical source for 2croslinking polymerisation Irganox 1010 hindered phenol thermal 0.1stabilizer for reverting polymer degradation manufactured by Ciba-GeigyCorp. DSTDP (Distearylthioldipropionate) 0.1 thioester secondaryantioxidant for preventing polymer degradation Ultranox 626 secondaryantioxidant from 0.05 Berg-Warner Chemicals B. (Back Layer) Exact 4038100 Magnesium Hydroxide 150 2,2-bis (tert. butylperoxy) Butane free 2radical source crosslinking polymerisation Irganox 1010 0.1 DSTDP 0.1Ultranox 626 0.05 C. (Foamable Layer) Exact 5008 100 Wollastonite highaspect ratio calcium 30 metasilicate reinforcing filler AluminumTrihydrate flame retardant 30 inorganic filer Azodicarbonamide chemicalfoaming agent 2 (giving off nitrogen gas) Zinc Oxide for loweringdecomposition 0.8 temperature of Azodicarbonamide to reduce polymer foamtemperature 2,2-bis (tert. butylperoxy) Butane 2 Irganox 1010 0.1 DSTDP0.1 Ultranox 626 0.05 Luchem HA-B18 polymeric hindered amine 0.15 lightstabilizer from Atochem for preventing polymer photo degradation D. (TopWear Layer) Exact 5008 100 Vinyltriethoxysilane, providing 4 additionalcrosslinking toughness and solvent resistance 2,2-bis (tert.butylperoxy) Butane 2 Luchem HA-B18 0.3 Irganox 1010 0.1 DSTDP 0.1Ultranox 626 0.05

EXAMPLE 2 Preparation of Multi-Layer Floor Covering Using Spread-Coating

[0095] In example 2, the same sequencing of steps and stations are usedas in Example 1, except that each application station involves a meltspreading operation rather than a melt calendering operation. Thecomposition of all the four layers is the same except that 80 parts ofJayflex 215 and 20 parts of monomer X980 (a crosslinking monomer fromRohm & Haas) are added to each of the four formulations.

[0096] It will be appreciated that various modifications may be made tothe above described embodiment with out departing from the scope ofpresent invention. Thus for example Electron Beam initiated crosslinkingcan be an alternative or supplemental process to chemically initiatedcrosslinking. Such crosslinking can be accomplished by subjecting asample to high-energy electrons at a dose of about 6 to 8 mega rads overa 30 second to 2 minute period. The addition of a reactive monomer suchas methylolpropane trimethacrylate (TMPTMA) at about 2 to 5 parts isuseful to get a good result from this process.

EXAMPLE 3 Individual Layer Formulations

[0097] The following polymer resin formulations have been prepared: PHRA. (Clear coat layer) MPO Resin Engage EP8500 (Dow Chemical Co.) 100 (MI5.0, Density 0.87, DRI 0.5) Irganox 1010 Antioxidant Stabiliser 0.05 BHTAntioxidant Stabiliser 0.03 2,5-TRI Cross-Linking Agent 0.1 B. (FoamableGel Layer) MPO Resin Engage EP 8500 (Dow Chemical Co.) 100 Whitingfiller (generic) 15 Azo blowing agent (generic) 3 Zinc oxide FoamingCatalyst 1.5 Titanium oxide pigmentation component 4 Irganox 1010Stabiliser 0.075 DSTDP Stabiliser 0.05 Calcium stearate Flowing Agent0.10 Firebrake (TM) flame retardant 5 Antimony oxide flame retardant 4C. (Saturant Layer) MPO Resin Engage EP 8500 (Dow Chemical Co.) 100Whiting filler (generic) 50 Irganox 1010 Stabilizer 0.1 Zinc stearateFlowing Aid 0.4 D. (Solid Backcoat Layer) MPO Resin Engage EP 8500 (DowChemical Co.) 100 Whiting filler (generic) 200 Titanium oxidepigmentation component 4 Irganox 1010 Stabiliser 0.075 DSTDP Stabiliser0.05 Calcium stearate Flowing Agent 0.10 Firebrake (TM) flame retardant5 Antimony oxide flame retardant 4

EXAMPLE 4 Individual Layer Formulations

[0098] A further set of polymer resin formulations is prepared as inExample 1 above but with Dow Chemical Co.'s Affinity SM 1250 as the MPOResin component in place of EP 8500.

EXAMPLE 5 Preparation of Multi-Layer Floor Covering Using MultipleSpreading

[0099] A floor covering material is prepared as a four layer structureby a multiple spreading application technique. At an initial station aglass fibre web is saturated with polymer having composition A at atemperature of approximately 100° C. At a separate station a backcoating of composition B is applied to the bottom side of the polymersaturated glass web at approximately 100° C. At another separate stationthe foamable layer, composition C, is applied to the top side of thepolymer saturated glass web at approximately 100° C. A decorativepattern is then printed upon the foamable layer using a continuousprinting process that employs, in one of several inks, benzotriazole, todeactivate the accelerated foaming system thereby to produce a chemicaldebossing effect upon foaming. In a further separate coating step of theprocess a clear wear layer of composition D is applied to the foamablelayer at approximately 100° C. The structure is then passed through aoven system to crosslink the layers at approximately 170° C. and thenexpand the foam layer to approximately 200° C. The final cured,decorated and embossed product constitutes the floor covering material.PHR A. (Saturant Layer) Exact 4038 MPO Resin 100 Calcium Carbonate 66.7Stearyl Methacrylate (settable plasticizer) 90 Trimethylolpropanetrimethacrylate 10 (settable plasticizer) Lupersol 230 (free radicalpolymerisation 5 initiator from Atochem) Irganox 1010 0.1 DSTDP 0.1Ultranox 626 0.05 B. (Backcoat Layer) Exact 4038 100 Calcium Carbonate300 Stearyl Methacrylate 90 Trimethylolpropane trimethacrylate 10Lupersol 230 5 Irganox 1010 0.1 DSTDP 0.1 Ultranox 626 0.05 C. (FoamableLayer) Exact 5008 100 Calcium Carbonate 66.7 Stearyl Methacrylate 90Trimethylolpropane trimethacrylate 10 Lupersol 230 5 Celogen OT(chemical Blowing agent 4 from Uniroyal) Zinc Oxide 2 Luchem HA -B180.15 Irganox 1010 0.1 DSTDP 0.1 Ultranox 626 0.05 D. (Wear Layer) Exact3017 100 Stearyl Methacrylate 70 Trimethylolpropane trimethacrylate 30Lupersol 230 5 Vinyl trimethosilane 4 Luchem HA -B18 0.3 Irganox 10100.1 DSTDP 0.1 Ultranox 626 0.05

1. A solid sheet suitable for use as at least one layer of a polymericfloor covering, wherein said solid sheet comprises a polyalkene resin inintimate admixture with at least one additive comprising a filler,wherein said polyalkene resin is a polyalkene resin obtained by a singlesite catalyzed polymerization of at least one, linear, branched orcyclic alkene having from 2 to 20 carbon atoms.
 2. A solid sheetaccording to claim 1, which polyalkene resin has a molecular weightdistribution of less than
 3. 3. A solid sheet according to claim 1wherein said polyalkene is one having the following characteristics: a)Melt Index of from 0.1 to 100 dg/minute; b) Density of from 0.86 to 0.97g/cm³; and c) a small amount of long chain branching which amount isdefined as a Dow Rheology Index of from 0.1 to 6.0 measured by comparingthe shift to the right, relative to a polymer resin with zero long-chainbranching, in a plot of zero shear viscosity against relaxation time. 4.A solid sheet according to claim 3 wherein said polyalkene resin has aDow Rheology Index of from 0.4 to 5.5.
 5. A solid sheet according toclaim 1 wherein said polyalkene comprises a copolymer obtainable bycopolymerization of at least two alkenes comprising a first, linear orbranched, alkene having from 2 to 8 carbon atoms and, at least onecomonomer, which comonomer comprises a linear, branched or cyclic,alkene having from 2 to 20 carbon atoms.
 6. A solid sheet according toclaim 5 wherein said first monomer comprises ethylene and said at leastone comonomer is selected from butene-1, hexane-1, and norbomene.
 7. Asolid sheet according to claim 5 wherein said comonomer is present in anamount of up to 15 mole percent based on the total amount of saidmonomer.
 8. A solid sheet according to claim 1 which includes a polymer,said polymer being obtainable by polymerization of a liquid plasticizermonomer system which is: (i) non-polymerizable under sheet formingconditions used in floor covering sheet material manufacture; (ii)whilst being polymerizable subsequently after forming of said intimateadmixture of said polyalkene resin, and said at least one additive,together with said polymerizable plasticizer monomer system into asheet, so as to produce a sheet material free of liquid plasticizermonomer, at least one of said polymer and said polyalkene resin beingcross-linked so that polymer chains of said polymer and polymer chainsof said polyalkene resin together form an at least semi-interpenetratingnetwork of polymer chains.
 9. A solid sheet according to claim 8 whereinsaid plasticizer monomer comprises a linear, branched or cyclic alkenehaving at least 10 carbon atoms and a polymerizable terminal functiongroup.
 10. A solid sheet material according to claim 1, which solidsheet is itself suitable for use directly as a polymeric floor covering.11. A solid sheet according to claim 1 which is free of liquidplasticizer.
 12. A process for the production of a solid sheet suitablefor use as at least one layer of a polymeric floor covering, saidprocess comprising the steps of: providing a polyalkene resin obtainedby a single site catalyzed polymerization of at least one, linear,branched or cyclic, alkene having from 2 to 20 carbon atoms and at leastone additive comprising an inorganic filler; bringing said polyalkeneresin into intimate admixture with said at least one additive in a highshear mixer for a period of at least 10 minutes at an elevatedtemperature of at least 75° C. for melting the polyalkenes andsufficient to bring the mixture into a fluid state without degradationof the mixture; forming the fluid mixture into a sheet form; andallowing said sheet to cool and solidify.
 13. A process according toclaim 12 which includes the further step of incorporating into themixture a sheet forming processing aid.
 14. A process according to claim12 wherein the sheet forming process comprises spread coating.
 15. Aprocess according to claim 14 wherein a liquid plasticizer is used as aspread coating aid in said spread coating step.
 16. A process accordingto claim 15 wherein a liquid paraffin is used as a spread coating aid insaid spread coating step.
 17. A process according to claim 13 whereinthe step of incorporating into the mixture a sheet formation processingaid comprises the further step of incorporating a polymerizable liquidplasticizer monomer system which is: (i) non-polymerizable under sheetforming conditions used in floor covering sheet material manufacture,while (ii) being polymerizable subsequently so as to produce a polymermaterial free of liquid plasticizer monomer.
 18. A process according toclaim 17 which process includes the further step of treating the sheetform material so as to induce polymerization of said liquid plasticizermonomer system thereby to produce a sheet material free of liquidplasticizer.
 19. A process according to claim 18 wherein said sheetforming step is carried out at from 70 to 120° C. and saidpolymerization step is carried out at from 150 to 250° C.
 20. A processaccording to claim 12 wherein the sheet forming process step comprisesthe further step of rolling said fluid mixture on a calendar.